French patent FR 2792460, which is known in the prior art, describes a photovoltaic generator comprising at least one photovoltaic cell and a transparent matrix deposited with at least one optically active material having an absorption wavelength lambdaa and a re-emission wavelength lambda, the optically active material being selected such that lambdaa corresponds to a range of lower sensitivity of the photovoltaic cell than lambdar, the matrix comprising a reflective coating. The matrix comprises, on the input surface, a dichroic filter substantially reflecting wavelengths of more than around 950 nm, and substantially transparent for wavelengths of less than 950 nm, and on the surface opposite the input surface a reflective coating for wavelengths of more than 400 nm, the photovoltaic cell being included in the transparent matrix.
U.S. Pat. No. 4,088,508, which is known in the prior art, describes an energy amplifying device that can be adapted to a solar cell, including a matrix with fluorescent substances dispersed therein.
U.S. Pat. No. 4,367,367 is also known, describing a collector suitable for concentrating solar energy on a photoelectric cell, including in combination at least one glass plate doped with a substance that is fluorescent when lit by sunlight. A photoelectric cell is attached to a lateral side of the plate, the other lateral sides of the plate being provided with a reflective coating. The cell is highly efficient in the fluorescent radiation wavelength range. A plurality of such glass plates can be stacked upon one another, each doped to absorb at a predetermined region of the spectrum and to fluoresce in a region in which a certain photoelectric cell is sensitive. A fluorescent dye in a suitable substrate can be applied as a surface layer on such glass plates, and this improves the overall efficiency of the collector.
U.S. Pat. No. 4,110,123 describes a photovoltaic cell, in which light is collected in a light concentrator including a transparent layer, the refraction coefficient of which is higher than that of the ambient medium and which contains fluorescent centres and is fed to a solar cell, characterised in that more than one concentrator/solar cell combination is stacked on top of another by means of a medium having a lower refraction coefficient than that of the concentrators, each concentrator being suitable for converting a portion of the incident spectrum into fluorescent light and for supplying same to a solar cell.
U.S. Pat. No. 7,541,537 describes a photovoltaic cell having improved conversion properties. The cell includes a cover for a photovoltaic device. In one embodiment, the cover includes a fluorescent material that shifts the wavelength of one portion of the incident light to be closer to the wavelength that produces the least amount of thermal loading on the photovoltaic device. In another embodiment, the cover comprises a fluorescent material between two reflective filters. The cell and the cover can be placed together in a stack or separated from one another.
The prior art solutions have problems of optical yield. When the matrix contains a plurality of dopants of various natures, the chemical or optical interactions thereof cause an attenuation or an alteration of the transmission in certain cases of high concentrations of dopants, or a loss of efficiency when the concentration of certain dopants is insufficient. An unsuitable concentration may even cause the extinction of certain re-emission phenomena, thus completely modifying the lighting spectrum produced by the doped interface. Furthermore, some of the prior art solutions propose a multi-layer interface formed by a stack of planes, each having a specific type of dopant. The disadvantage of said solutions is that the interactions take place in sequential fashion and do not enable the creation of enough interactions to have any real effect of optimising the lighting spectrum.